A liquid propellant gun and a method of controlling liquid in a combustion or liquid propellant gun is disclosed. The gun is provided with a barrel attached to the receiver having a cavity formed therein, which is coupled to the barrel or throat. A guide tube coaxially extends through the receiver cavity bisecting the cavity into a main chamber and essential axially passageway. The guide tube has at least one orifice extending therethrough connecting the main chamber to the essential passageway. An elongated pin is telescopically shiftable within the guide tube to load projectiles into a firing position seated in the barrel throat. A projectile, when in the barrel throat defines a prechamber abounded by the guide tube. Liquid propellant is admitted into the chamber and ignited within the prechamber causing the prechamber pressure to rapidly rise forcing hot combustion products into the main chamber and causing the pin to begin to retract. The propellant in the main chamber then burns and the combustion is regulated in part by the pin position.